Unlocking the Mysteries of the Universe: Hubble, Webb, and the Cosmic Distance Scale

2024-03-28 03:55:16

This image of NGC 5468, a galaxy located about 130 million light-years from Earth, combines data from the Hubble and James Webb space telescopes. It is the most distant galaxy in which Hubble has detected Cepheid variable stars. These are important milestones for measuring the expansion rate of the universe. The distance calculated from Cepheids is cross-correlated with the type Ia supernova in the galaxy. Type Ia supernovae are so bright that they are used to measure cosmic distances far beyond the cupid range, extending measurements of the universe’s expansion rate deeper into space. Credit: NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)

A discrepancy in the measurement of the Hubble constant, known as the Hubble stress, has been a significant puzzle in cosmology. The James Space Telescope and with the approval of the Abel Space Telescope, the Cosmic Distance Scale data established the Duke Cosmic Distance Scale data and suggested that the discrepancy may imply unknown cosmic phenomena, which requires further investigation.

The rate at which the universe expands, known as Hubble’s constant, is one of the basic parameters for understanding the evolution and ultimate fate of the cosmos. However, a persistent difference, called the Hubble stress, is seen between the value of the constant measured with a wide variety of independent distance indicators and its value predicted from the post-Big Bang flow. NASA/ESA/CSA space telescope James Webb has confirmed that the sharp eye of the Hubble Space Telescope was right all along, erasing any lingering doubts about Hubble’s measurements.

The historic achievements of Hubble

One of the scientific justifications for building the NASA/ESA Hubble Space Telescope was to use its observational power to provide an accurate value for the expansion rate of the universe. Before Hubble’s launch in 1990, observations from ground-based telescopes yielded huge uncertainties. Depending on the values ​​derived for the expansion rate, The universe could be between 10 and 20 billion years old. Over the past 34 years, Hubble has narrowed this measurement to less than one percent accuracy, splitting the difference with an age value of 13.8 billion years. This was achieved by refining the so-called ‘Cosmic Distance Scale’ on By measuring important milestones known as Cepheid variable stars.

Treating the stress of grieving with Webb

However, Hubble’s value does not agree with other measurements that suggest the universe expanded more rapidly after the Big Bang. These observations were made by the ESA Planck satellite’s mapping of the cosmic microwave background radiation – a blueprint for how the universe will develop structurally after it cools from the Big Bang.

The simple solution to the dilemma would be to say that maybe Hubble’s observations are wrong, as a result of some inaccuracy creeping into the measurements of deep space standards. Then came the James Webb Space Telescope, which allowed astronomers to cross-reference Hubble’s results. Webb’s infrared views of Cepheids matched Hubble’s optical light data. Webb confirmed that Hubble’s sharp eye was right all along, erasing any lingering doubts about Hubble’s measurements.

In the center of these side-by-side images is a special class of stars that serves as a marker for measuring the expansion rate of the universe – a Cepheid variable star. Both images are highly pixelated because they are a highly magnified view of a distant galaxy. Each of the pixels represents one or more stars. The image from the James Webb Space Telescope is significantly sharper at near-infrared wavelengths than the Hubble (which is primarily an ultraviolet light telescope). By reducing the clutter with Webb’s strong vision, the cupid stands out more clearly, eliminating any potential confusion. Webb was used to look at a sample of cupids and confirmed the accuracy of previous Hubble observations that are fundamental to accurately measuring the expansion rate and age of the universe. Credit: NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)

Cosmic mysteries and theoretical challenges

The bottom line is that the so-called Hubble tension between what’s happening in the nearby universe compared to the expansion of the early universe remains a vexing puzzle for cosmologists. There may be something woven into the fabric of space that we have not yet understood.

Does solving this gap require new physics? Or is it the result of measurement errors between the two different methods used to determine the rate of space expansion?

Hubble and Webb have now teamed up to produce definitive measurements, furthering the case that something else – not measurement errors – is affecting the rate of expansion.

Advances in Cosmic Observations

“With measurement errors eliminated, what remains is the very real and exciting possibility that we have misunderstood the universe,” said Adam Rees, a physicist at Johns Hopkins University in Baltimore. A man holds the Nobel Prize for the joint discovery of the fact that the expansion of the universe is accelerating, due to a mysterious phenomenon now called ‘dark energy’.

As a cross-check, Webb’s initial observation in 2023 confirmed that Hubble’s measurements of the expanding universe were accurate. However, hoping to ease the stress of grieving, some scientists have speculated that invisible errors in measurement may grow and become visible as we look deeper into the universe. In particular, stellar density can systematically affect brightness measurements of more distant stars.

Collaborative validation and future directions

The SH0ES (Dark Energy Equation of State Supernova H0) team, led by Adam, obtained additional observations with Webb of objects that are critical cosmic mile markers, known as Cepheid variable stars, which can now be correlated with the Hubble data.

“We have now spanned the entire range of what Hubble observed, and we can rule out measurement error as the cause of the Hubble voltage with very high confidence,” Adam said.

The first observations by the Webb team in 2023 were able to show that Hubble is on the right track in faithfully establishing the first steps of the so-called cosmic distance scale.

This figure shows the three basic steps astronomers use to calculate how fast the universe is expanding over time, a value called Hubble’s constant. All steps involve building a robust “cosmic distance scale” by starting by measuring precise distances to nearby galaxies and then moving to increasingly distant galaxies. This “scale” is a series of measurements of different types of astronomical objects with intrinsic brightness that researchers can use to calculate distances. Among the most reliable at shorter distances are Cepheid variables, stars that pulsate at predictable rates that indicate their intrinsic luminosity. Astronomers recently used the Hubble Space Telescope to observe 70 Cepheid variables in the nearby Large Magellanic Cloud to make the most accurate distance measurement to that galaxy. Astronomers compare the measurements of nearby cupids with those in more distant galaxies, which also include another cosmic benchmark, exploding stars called Type Ia supernovae. These supernovae are much brighter than Cepheid variables. Astronomers use them as “landmarks” to gauge the distance from Earth to distant galaxies. Each of these markers builds on the previous step in the “ladder”. By expanding the scale using different types of reliable waypoints, astronomers can reach very large distances in the universe. Astronomers compare these distance values ​​to measurements of the light of an entire galaxy, which dims more and more with distance, due to the uniform expansion of space. Astronomers can then calculate how fast the cosmos is expanding: Hubble’s constant. Credits: NASA, ESA and A. Feild (STScI)

The intricacies of the cosmic distance scale

Astronomers use different methods to measure relative distances in the universe, depending on the object being observed. Together these techniques are known as the Cosmic Distance Scale – each step or measurement technique relies on the previous step for calibration.

But some astronomers have suggested that as it moves outward along the ‘second phase’, the cosmic distance scale could be shaken if cupid measurements become less accurate with distance. Such inaccuracies can occur because a Cepheid’s light can blend with that of a nearby star—an effect that can become more pronounced with distance when stars are crowded in the sky and harder to distinguish.

The observational challenge is that past Hubble images of more distant Cepheid variables appear more crowded and overlapping with neighboring stars at greater and greater distances between us and their host galaxies, requiring careful consideration of this effect. Interfering dust further complicates the certainty of visible light measurements. Webb cuts through the dust and naturally isolates the Cepheids from neighboring stars because its vision is sharper than Hubble’s at infrared wavelengths.

“The combination of Webb and Hubble gives us the best of both worlds. We find that Hubble measurements remain reliable as we climb further along the cosmic distance scale,” Adam said.

Webb’s new observations include five host galaxies of eight Type Ia supernovae containing a total of 1000 cupids, and reach the most distant galaxy where cupids have been well measured – NGC 5468, 130 million light-years away. “It spans the entire range where we’ve made measurements with the Hubble. So, we’ve gone to the end of the second rung of the cosmic distance scale,” said co-author Gagandeep Anand of the Space Telescope Science Institute in Baltimore, which operates the Webb and Hubble telescopes for NASA.

Together, Hubble and Webb’s confirmation of the Hubble strain sets up other observatories to possibly solve the mystery, including NASA’s upcoming Nancy Grace Roman Space Telescope and ESA’s recently launched Euclid mission.

Right now it’s as if the distance scale observed by Hubble and Webb set an anchor point on one shoreline of a river, and the glow of the big bang observed by Planck from the beginning of the universe is firmly placed on the other. How the expansion of the universe changed in the billions of years between these two endpoints has yet to be directly observed. “We need to find out if we’re missing something on how to connect the beginning of the universe and today,” Adam said.

These findings were published in the February 6, 2024 issue of The Astrophysical Journal Letters.